Method for dry sorting the constituents of a homogeneous mixture



c E. Home 3,407,929

METHOD FOR DRY SOR'IING THE CONSTITUENTS OF A HOMOGENEOUS MIXTURE FiledFeb. 20, 1967 Oct. 29, 1968 haw/v r01? Claw-nu: t2 amur l Ali/# UnitedStates Patent 3,407,929 METHOD FOR DRY SORTING THE CONSTITUEN TS OF AHOMOGENEOUS MIXTURE Christine Elisabeth Hoing, Rue de Beaupreau 29,Sainte-Genevieve, France Filed Feb. 20, 1967, Ser. No. 617,301

Claims priority, application France, Mar. 1, 1966,

51,423; Aug. 5, 1966, 72,181

4 Claims. (Cl. 209-3) ABSTRACT OF THE DISCLOSURE The constituents of ahomogeneous granular mixture are dry sorted by passing the mixture downa first inclined perforated chute, blowing a gas through theperforations in the chute to fluidize the granular particles and passingthe fluidized mixture down a second inclined perforated chute alongwhich the granular particles are sorted and deposited through theperforations according to their specific weights.

According to the present invention there is provided a method for drysorting the constituents of a homogeneous mixture.

When a homogeneous mixture of heterogeneous granular substances ofdifferent specific weights are placed on a sloping surface, the mixturetends to flow down the surface due to the force of gravity and due tothe heavier particles being concentrated in the lower layers of thestream and the lighter higher layers toppling over the lower heavierlayers.

A similar result is obtained by subjecting a homogeneous mixture to anupwardly directed stream of gas passing through said mixture.

However, in the present state of the art, dry sorting a homogeneousmixture in accordance with the specific weights of the constituentgranular particles by using either of the above principles applied aloneor in combination has not found any satisfactory practical solution.

A combination of the two principles is sometimes effected when it isrequired to remove the heavier product located in the lower portion ofthe stream of the granular products through a succession of portslocated in the area subjected to a blast of air. However, the extractionthus performed disturbs considerably the sorting of the products in theactual area in which said extraction is executed, which leads to areduction in the efficiency of the sorting procedure.

Considering the constituents of an initial mixture of granular particlessorted in accordance with their specific weights, I will term efficiencyof the sorting executed in accordance with my invention as the ratio ofthe weight of the granular particles of a constituent in the mixture andthe weight of the granular particles of the constituent which haveactually been sorted from the mixture, disregarding the particles whichshould have been incorporated with other sorted constituents.

An object of my invention is to obtain a high efficiency.

Further objects of my invention consist in providing a sorting methodwhich is also economical in energy expenditure and in providing asorting method which may be conveniently executed in a static plant. Astill further object consists in retaining the product in a drycondition without requiring as in the case of the moist methods, anysubsequent drying.

The perfecting of my invention has been obtained by an accurateinvestigation of sorting mechanisms and by investigating the conditionsof sorting a homogeneous mixture in accordance with the specific weightof solid granular particles of its constituents firstly when the mix-"ice ture flows over a sloping surface and secondly it is subjected to aflux of a gas stream rising upwardly through it.

The investigations have shown that sorting by merely flowing the mixtureover a sloping surface is practically possible only for mixtures ofshallow depth, While the required slope of the surface over which theparticles flow depends on the granulometric structure of the mixture.

My investigations have shown furthermore that the optimum sortingobtained through blowing gas through the mixture requires that the speedof the gas through the mixture should be maintained at a. constant valuewithin comparatively narrow limits for all the points of the masssubjected to the gas and that its optimum value depends on the densityof the constituents of the mixture.

The investigations have also shown that the most efiicient results havebeen obtained through the suitable combination of the above conditions.

According to the present invention there is provided a method of drysorting mixtures of solid granular particles of different specificweights in accordance with their specific weights, consisting in a firststage causing the mixture to flow under the action of gravity over aporous sloping surface, blowing a gas through said porous slopingsurface to fluidize the stream of granular particles causing stream ofgranular particles to slide during a second stage over a perforatedsloping surface through which the sorted particles drop in succession inaccordance with the succession of their specific weight.

The stream flowing over the porous surface may have a suitable thicknessranging between 3 and 30 times the average size of the granules andranges preferably between 3 and 15 times said size.

In order to ensure a uniform speed at all points of the gas stream, theporous surface over which the mixture flows preferably has portsdistributed as close to one another as possible, while the size of eachport is preferably smaller than that of the finest particles.

The pressure applied to the stream of particles is preferably the lowestrequired for fluidizing it Without any deviation of the upper particlesout of the stream.

The slope given to the porous sorting surface is preferably the minimumrequired to produce a uniform progression of the particles at all pointsthereof.

The slope given to the lower separating grid also is preferably theminimum required for reliably producing a uniform flow of the streampassing off the porous surface.

Embodiments of my invention will now be described by way of example withreference to the accompanying drawings, in which:

FIGURE 1 is a vertical longitudinal cross-section of the plant accordingto my invention, showing a sorting channel.

FIGURE 2 is a vertical longitudinal cross-section of the sorting channelprovided with a separating grid.

FIGURE 3 is a plan view of the Whole arrangement including the sortingchannel and separating grid.

FIGURE 4 is a vertical cross-section of a modified embodiment of asorting channel.

The arrangement in which the mixture is subjected to a sorting treatmentincludes, as illustrated in FIGURES 1 and 2 a sorting channel 1 of arectangular cross-section of which the fiat bottom 2 is made of finelyporous material. Under said bottom, there is provided a pipe 3 throughwhich a gas, for example air, is blown under a uniform pressurethroughout the bottom 2.

The channel 1 is set in a manner such that its porous bottom surface mayslope by a predetermined angle a with reference to a horizontal plane.The granular mixture 14 to be sorted is introduced into the channel soas to flow down towards a lower section under the double action of theslope defined at a and of the fiuidization produced by blowing. For asame mixture, the efiiciency of the classification according to specificweights obtained at the lower end of the channels depends on the anglea, on the value of the pressure of the fluidizing gas taking intoaccount the permeability of the porous surface and length of the channeland the input of solid material entering the channel; said values mustbe adjusted experimentally with reference to each other in accordancewith the abovedefined values with a view to obtaining an optimum result.To this end, the channel may be set by any suitable known means at anangle of slope a which may be adjusted and measured, while the pressureis supplied at adjustable or measurable values depending on the porosityof the bottom and on the dissymmetric composition of the mixture. Theinput of granular particles is also adjusted to a suitable value througha modification of the thickness of the stream of granular particles. Thechannel length is defined experimentally beforehand as a function of thenature of the products to be sorted with a view to obtaining a maximumefficiency.

Experience has shown that large differences between the specific weightsof the constituents of the mixture to be sorted allow reducing thechannel length. If the differences are small said length should beincreased.

The channel is of uniform width and is defined as a function of thedesired input of solid material by weight taking into account thethickness of the mixture stream and the average specific weight of themixture to be treated. The width may, if required, be reduced as shownin FIGURE 3 by means of a movable flange 5 of a suitable thicknessengaging both sides of the channel.

In order to collect separately at the output end of the channel theconstituents which have been classified according to their specificWeights during their progression along the channel and which are nowarranged in layers of specific weights decreasing from bottom to topwithin the thickness of the stream of fluidized particles, at the lowerend of the channel there is provided a further channel 6 including aseparating grid (FIGURES 1, 2, 3). The bottom of said channel 6 isconstituted by a slotted or perforated grid 7 wherein the openings aresized so as to match the granulometric composition of the products whichare to pass through it. Said channel 6 is set in a manner such that thegrid 7 slopes with reference to a horizontal plane by an angle b whichmay be adjusted with reference to the angle a of the slope of thechannel 1 in accordance with the nature of the mixture undergoingtreatment and the speed of the mixture as it passes out of the sortingchannel 1 to ensure a flow at a preferably minimum speed over theseparating grid 7.

Under such conditions, there is obtained through the grid 7 insuccessive portions of the channel 6 a longitudinal classificationunderneath the channel 6 of the layers of a decreasing weight which wereactually distributed vertically within the thickness of the stream offluidized particles at the output of the channel 1 with an optimumefficiency.

The separation of the different components into as many fractions as maybe required in practice may be obtained by arranging underneath the gridflaps 8 which are given a suitable slope, so as to allow the differentconstituents to be collected to drop into separate containers 9.

The flaps 8 are preferably movable throughout the length of the grid 7,so that it is possible to adjust the grid length corresponding to eachconstituent in accordance with the requirements of the mixture to besorted and thereby to adjust the composition of each of saidconstituents.

It is of advantage to restrict gradually the breadth of the stream ofgranular particles over the grid as they progress from the input endtowards the output end of the grid so as to take into account thegradual decrease of the throughput of granular particles over the grid.

This result may be obtained by way of example in a non-limiting sense asillustrated in FIGURE 3 by two blades 10 perpendicular to the plane ofthe grid which may be laid over the latter so as to assume the shape ofa V the opening of which is adjustable through a flexing or a pivotalmovement of said blades about their points of attachment to the sides ofthe grid at the input end thereof.

Various other modifications of this mixture constituent classifyingarrangement may be contemplated all of which draw the classifiedproducts out of classified superposed layers of different specificweights extending substantially in horizontal planes.

In certain particular cases depending on the nature of the mixture to besorted, it is of advantage to accelerate the speed of flow of the upperlayer of the stream. Said may be achieved for instance (FIGURE 4) byclosing completely or partly by a plate 12 the upper surface of thesorting channel 1.

This results in producing in parallelism with the stream of granularparticles a stream of gas tapped off the gas fiow blown through thechannel bottom and sweeping at a higher speed along the upper surfacelayer of granular particles. Said speed of flow of the gas andconsequently of the granular particles in said surface layer may beadjusted through a vertical shifting of the plate 12 the plane of whichmay be parallel with that of the porous bottom 2 or may slope withreference to the latter, so as to provide an adjustable cross-sectionfor the flow of the stream of air. It is possible, if required, toincrease said speed of flow through a further admission of compressedair under a suitable pressure fed out of a pipe 13 (FIG- URE 4), whichair is admixed with the air blown through the bottom of the channel 1;it is also possible in contradistinction to reduce the flow of air byclosing only a portion of the upper surface of the channel for instanceby having a plate 12 which is suitably perforated.

Preferably the porous sloping bottom of the channel 1 comprises an upperlayer of the material sold under the registered trademark nylon, saidlayer :being carried by a metal gauze and by a lower sheet of felt.

The slope of the porous channel 1 is adjustable preferably between 8 and25. While the slope of the perforated channel 6 is adjustable preferablybetween 20 and 40.

For industrial or commercial purposes, preferably a plurality ofarrangements may be connected in series each including a sorting channeland separating grid, according to the well-known sorting method for therenewed treatment of intermediate or compound constituents.

I will now give by way of example the results obtained with my improvedmethod.

Example 1 The mixture to be treated is a sand of a granulometriccomposition ranging between 0.15 and 0.35 mm. Its composition asconcerns specific weights is as follows:

Percent (a) Specific weight 2.6 (silica) 43.2 (b) Specific weight about3.5 (staurotide and/or garnet) 7.8

The treatment is performed in a sorting channel of a width of 10 cm. andof a length of cm. forming an angle of 105' to the horizontal, under apressure of blown in air equal to 9 cm. of a water column. Theseparation is performed over a grid provided with slots of a width of1.2 mm., sloping at 31 with reference to a horizontal plane. Fourfractions are collected after a single passage through the channel witha throughput of 1,080 kg. per hour.

The following tabulae show the distribution of the four fractions F1,F2, F3, F4, being the percentages by weight of the total mixture treatedand the composition as to (c) Specific weight 4.6 (ilmenite and/ orzircone) specific weight for each fraction as compared with thecomposition of the mixture.

The preceding fraction F1 is treated again in the same channel with athroughput of 1,120 kg. per hour. After a single passage two fractionsare collected F1 and F2, of which the compositions are as follows:

Initial F1 F2 mixture Proportions of the fractions by weight 100% 60%40% Distribution of the specific weights:

Example 3 Concentrated heavy ore consisting of granular particlesranging between 0.15 and 0.40 mm., is treated in the same channel as forthe preceding examples, sloping at 8 to the horizontal in a stream ofair flowing under a pressure equal to 7 cm. of a water column while thethroughput of solid material is equal to 1,160 kg. per hour.

Initial composition as to specific weights Percent (a) Specific weight4.5 (ilmenite and/or zircone) 89 (b) Specific weight 5.1 (monazite) 11Three fractions F1, F2 and F3 are collected during a single passage inthe channel.

The following table discloses the results:

Mixture F1 F2 F3 treated Distribution by weight 100% 34% 54% 12%Composition as to specific Weight a--- 89 77 94 99. 5 11 23 5. 9 0. 5Distribution of the product having a specific weight equal to 5.. 100%74% 29% 0.06%

I claim:

1. A method of dry sorting mixtures of solid granular particles ofdifferent specific weights in accordance with their specific weights,comprising the steps of establishing a fluidized bed of mixed granularparticles to be sorted above a stationary porous inclined surface withthe angle of inclination of the porous surface only enough to cause thefluidized bed to move down along said porous surface by gravity untilsaid particles have vertically stratified into superposed layers whosedensity decreases from bottom to top, feeding the stratified particlesfrom the lower end of said porous surface to an upper portion of astationary inclined separating surface having a series of openingstherethrough larger than the size of the largest particles to beseparated while maintaining the path of the particles unimpeded abovesaid porous and separating surfaces with the angle of inclination ofsaid separating surface greater than that of said porous surface andonly enough to cause the particles to move down along said separatingsurface by gravity, maintaining the pressure below said separatingsurface no higher than atmospheric, and separately collecting aplurality of fractions of different density below different portions ofsaid separating surface lengthwise along said separating surface.

2. A method as claimed in claim 1, in which said fluidized bed isestablished by blowing a gas upward through said porous inclined surfaceunder constant pressure.

3. A method as claimed in claim 1, said fluidized bed having a thicknessfrom 3 to 30 times the average size of the granular particles.

4. A method as claimed in claim 1, said fluidized bed having a thicknessfrom 3 to 15 times the average size of the granular particles.

References Cited UNITED STATES PATENTS 1,068,162 7/1913 Payne 209-4662,093,470 9/1937 Morgan 209-474 2,303,367 12/1942 Kendall et al. 209-442,813,630 11/1957 Morrow 209474 2,903,132 9/1959 Berry 209-475 X3,007,577 11/1961 Putman 209474 X HARRY B. THORNTON, Primary Examiner.

TIM R. MILES, Assistant Examiner.

